ゾルゲル自己燃焼法により作製したナノニッケルフェライト粒子の低温生成プロセスの解明および磁気特性

概要

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Nano-crystalline NiFe2O4 (NF) powder was prepared by a sol-gel auto-combustion method. Its crystal structure, morphology, particle size and magnetic properties were investigated and the formation process of nano-crystalline NF was elucidated. The as-dried Ni-Fe precursor (Ni/Fe=0.5) was calcined in air at 200-800°C for 4 hours. γ-Fe2O3 powder was formed at about 210°C by the self-combustion of the gel, and was maintained at 200-400°C. Single-phase NF sample was obtained by being calcined at 600-800°C. The NF particles were of nano-crystalline with crystallite diameters of 68.2-94.3 nm which were determined by the use of Scherrer equation for XRD peak broadening and the observation of TEM images. The sample calcined at 200°C had a magnetization value of 44 emu/g, which was lower than that of bulk γ-Fe2O3 (70 emu/g) because of a lot of vacancies at octahedral sites. Magnetization was increased gradually with increasing calcination temperature, and reached to the maximum value of 46 emu/g for the samples calcined at 700 and 800°C, which was in agreement with the magnetization of the bulk NF sample. Coercivity was decreased with increasing calcination temperature.